This invention is in the field of implantable blood filtering devices, and more specifically it is directed to filtering devices for implantation in arteries supplying blood to the brain. The invention is also concerned with a method for detecting and removing plaque debris from the filtering device.
Blood to the brain hemispheres is supplied by two carotid arteries, each of which branches-off into a so-called internal carotid and an external carotid. Blood to the brain stem is supplied by two vertebral arteries.
Cerebralvascular diseases are considered among the leading causes of mortality and morbidity in the modern age. Strokes denote an abrupt impairment of brain function caused by pathologic changes occurring in blood vessels. The main causes of strokes is insufficient blood flow to the brain (referred to as xe2x80x9can ischemic strokexe2x80x9d) which are about 80% of stroke cases.
Ischemic strokes are caused by sudden occlusion of an artery supplying blood to the brain. Occlusion or partial occlusion (stenosis) are the result of diseases of the arterial wall. Arterial atherosclerosis is by far the most common arterial disorder, and when complicated by thrombosis or embolism it is the most frequent cause of cerebral ischemia and infarction, eventually causing the cerebral stroke.
Such disorders are treated in different ways such as by drug management, surgery (carotid endarterectomy) in case of occlusive disease, or carotid angioplasty and carotid stents as known in the art.
While endarterectomy, angioplasty and carotid stenting are procedures targeting at reopening the occluded artery, they do not prevent progression of new plaque (restenosis). Furthermore, embolisms from the new forming plaque in the internal carotid artery (with or without a stent implanted therein) can occlude smaller arteries in the brain and cause strokes. Even more so, the above treatment methods do not prevent proximal embolic sources, i.e. embolus formed at remote sites (heart and ascending aorta) to pass through the reopened stenosis in the carotid and occlude smaller arteries in the brain.
It will also be appreciated that endarterectomy is not suitable for intracarnial arteries or in the vertebrobasilar system since these arteries are positioned within unacceptable environment (brain tissue, bone issue) or are of a small diameter.
Introducing filtering means into blood vessels has been known for a while, in particular into veins. However, such filtering means are generally of a complex design which render such devices not suitable for implantation with carotid arteries and not suitable for handling fine plaque debris. However, when considering the possible cerebral effects of even fine plaque debris occluding an artery supplying blood to the brain, the consequences may be fatal or cause irreversible brain damage.
Occlusion of a vein is not a critical event and in most cases a time range of up to several hours is available before severe damage is caused to organisms. This applies also to arterial blood supply to the heart, which may survive a longer period of time before critical damage is caused.
However, in light of the short periods of time during which brain tissue can survive without blood supply (several minutes only, typically about 3 minutes), there is significant importance to provide filtering means suitable for entrapping even small plaque debris to prevent brain damage.
Whilst a large variety of patents in the field of inplantable filtering systems are known to Applicants, they are mostly intended for implantation in veins and in particular are intended for vena cava implantation. The following is a list of U.S. Pat. Nos., all being in the field of implantable blood filters: U.S. Pat. Nos. 5,391,196, 5,626,605, 5,827,324, 4,425,908, 3,996,938, 4,494,531, 4,619,246, 4,873,978, 4,817,600, 4,943,297, 4,957,501, 4,990,156, 5,059,205, 5,152,777, 5,324,304, 5,344,425, 5,370,657, 5,413,586, 5,549,626, 5,649,950, 5,695,519, 5,720,764, 5,800,525, 5,814,064, 5,800,525 and 5,709,704.
It is noted, however, that neither of the above patents refers to hemodynamic considerations which as appreciated by a skilled person are of critical importance. This is one of the reasons why, so far, filtering devices for implantation into carotid arteries are not available.
By using the term xe2x80x9chemodynamicsxe2x80x9d it is referred to blood flowing parameters which if not maintained may be fatal. Such parameters are, for example, wall shear stress, shear rates, pressure drop over the filter, platelet activation parameter (which is the dominant parameter governing blood coagulation). It is thus essential that such a filtering device does not change the hemodynamic parameters beyond some predetermined parameters.
It is the object of the present invention to provide an implantable filtering device for positioning in a blood vessel supplying blood to the brain so as to filter the blood and entrap embolic debris and thereby prevent extracranial embolus to occlude small intracranial arteries in the brain.
It is a second aspect of the present invention to provide a method for detecting plaque debris entrapped within the filtering device and a method for removal thereof.
According to the present invention there is provided an implantable filtering device for implanting within an artery supplying blood to the brain the device being made of bio-compatible material and comprising a filtering unit for entrapping plaque debris, and an anchoring member engageable with the walls of the carotid artery for anchoring said filtering unit at a fixed location within the artery;
the filtering device is characterized in that the filtering unit has a tapering shape extending between a wide inlet portion and a narrower outlet portion extending downstream, said outlet portion comprising a trap element for entrapping plaque debris.
The term xe2x80x9ccarotid arteryxe2x80x9d denotes any of the main arteries supplying blood to the brain. However, a preferred site for implanting such a filtering device would be the internal carotid artery, although not restricted thereto. Implanting a filtering device may also be possible within the carotid artery branches and in the vertebrobasilar system.
The device in accordance with the present invention is designed to retain some hemodynamic parameters and accordingly, the filtering unit is formed with a plurality of openings which are sized, shaped and disposed so as to ensure the following parameters:
i) 2 less than wall shear stress less than 102[dynes/cm2]
ii) shear rate less than 5000 [secxe2x88x921]
however, preferably, the shear rate is smaller than 2000 [secxe2x88x921]. Furthermore, the pressure drop over the filtering device does not exceed about 20 mm Hg.
In a typical surgical procedure, the filtering device of the present invention is adapted for implanting within an internal carotid artery.
The trap element is adapted for trapping plaque debris which are filtered through the filtering unit. The trap element is a tubular body fixed to the filtering unit and comprises a plurality of deflectable trapping members radially extending within the body. The trapping members may also be arranged in a helical manner, extending inwardly from inner walls of the trap element. In accordance with one specific design, the trapping members constitute a maze and at a downstream end of the trapped member there are provided a plurality of deflectable end wires laterally extending across the end. In accordance with a most preferred embodiment, the trap element is cylindrical and coaxially extends at the outlet portion of the filtering unit. This particular design has significant importance in measuring flow parameters such as blood motion spectral signature and blood velocity profile. The trap element may also be formed with openings which may alternate in shape, depending on the desired flow pattern.
The arrangement is such that the end wires constitute a grid suitable for entrapping particles larger than about 100 xcexcm. The trapping members and the end-wires of the trapped element are deflectable to removably accommodate a guide wire (catheter) therethrough for inserting and positioning the filtering device in sight.
By one particular application the trapping members are actually elastically deflectable to facilitate insertion of a vacuum catheter for suction of plaque debris entrapped within the trap element. This is a procedure which may be carried out periodically or upon detection of change of either or both the blood velocity profile and the blood motion spectral signature by means of non invasive detection means, such as ultrasound or micro CT equipment, as known per se.
In accordance with a preferred embodiment of the present invention, the filtering unit is made of a sheet of material formed with a plurality of openings. By one particular design, the openings of the filtering unit are horseshoe-like shaped oriented such that the legs thereof are upstream, which has performed improved hemodynamic performances. In accordance with still a preferred embodiment, at least part of the openings are formed with a flow directing element outwardly and inwardly projecting from the surface of the filtering unit. In the case of openings formed in the horseshoe-like shape, these flow directing elements are constructed by the middle portion thereof which are outwardly (or inwardly, respectively) directed.
The design of the filtering openings has influence on different blood flow parameters such as decrease of stagnation zones, prevention or decrease of pressure drop, prevention or decrease of flow detachment (thus prevention of swirls and vortices), control of filtration property, control of flow (velocity profile distribution) and its derivatives such as sheer stress, and controlling the flow profile over the filtering device and at its flow wake.
In accordance with one embodiment of the invention the anchoring member is integrally formed with the filtering unit. Alternatively, the filtering unit is removably connected to the anchoring member by leg members. In accordance with some preferred embodiments, the anchoring member is a stent as known per se which extends upstream with respect to said filtering unit.
In accordance with one preferred design, the engaging member is essentially cylindrical and is formed with at least two shell-like segments. In accordance with a particular design, one or more of the at least two segments are outwardly biased and are adapted for engagement with inner walls of the artery in which the device is implanted.
Typically, the filtering device is suitable for entrapping plaque debris larger than about 100 xcexcm. The filtering unit may be designed in a variety of shapes, e.g. a wire braid essentially in the shape of a thimble, or a cone. Alternatively, the filter member may be a mashed screen made for example of Gortex(trademark), or of an inert metal. The openings of the screen may have any practical shape e.g., triangular, rectangular, round, etc.
For practical reasons, the maximal diameter of a device which may be transferred through the arteries is about 3 mm. Accordingly, at least a portion of the filtering unit, and the anchoring member are inserted into the carotid artery at a collapsed state and are then deployed into an extended, operative position. Accordingly, at the collapsed state, the portion of the filtering unit and the anchoring member are received within a removable insertion tube. For that purpose, at the collapsed state the portion of the filtering unit and the anchoring member are wrapped in an overlapping manner about a longitudinal axis of the device. Alternatively, at the collapsed position, the portion of the filtering unit and the anchoring member are axially sectioned, with at least one of the sections being wrapped in an overlapping manner about the longitudinal axis.
It will be noted that portions of the filtering device which are less than about 3 mm in diameter do not have to be collapsed and accordingly, the filtering device may be constructed of two portions, a first, downstream portion which does not have to be collapsed and a second, upstream portion which includes a wider inlet portion of the filtering unit and the anchoring member which are collapsed prior to introducing into the arterial system.
According to one specific embodiment, one or both of the anchoring member and at least the portion of the filtering unit are self-expendable. This may be obtained by using suitable materials or designing the device at a special structure. Alternatively, one or both of the anchoring member and at least the portion of the filtering unit are balloon expandable.
Both these methods are known in the art of stent implantation. The filtering device of the invention may be introduced into the carotid artery either by percutaneous technique or at endarterectomy, also as known per se and as dictated by medical considerations.
In accordance with one specific embodiment, the filtering unit is retained within the stent as a replaceable member. In accordance with this embodiment, the filtering unit is essentially in the shape of a thimble, cone or dome and has at its edge two or more hook members for attachment within the stent. By another specific embodiment, the filtering unit is essentially in the shape of a thimble, a cone or a dome and has a tapering open end portion adapted for anchoring within a narrowing portion of the stent. However, both embodiments may be applied together. In accordance with such embodiments, the filtering unit is removable from the stent by collapsing the tapering portion thereof so as to disengage from the stent. Accordingly, the filtering unit may be withdrawn for replacement.
By another aspect of the present invention, there is provided a device for removing or replacing a filtering unit of the type which is removably anchored within the stent. Such a device comprises at least two flexible hooking members each formed with a sliding portion normally biased into radial expansion and terminating at a hook suitable for engaging the tapering portion of the filtering unit, the hooking members being displaceable between a retracted position and an expanded position; a manipulating collar slidingly engaged with the sliding portions; whereby axial displacement of the manipulating collar entails displacement of the hooking members, so as to engage, retract and then withdraw the filtering unit, and if required replace it by a new one.
Still another aspect of the invention is concerned with a method for detecting plaque debris entrapped within the trap element and removal thereof. In accordance with this method, the blood velocity profile and the blood motion spectral signature are detected by non invasive means such as ultrasound, micro CT, etc., and upon detecting the presence of plaque debris within the trap element, a suction catheter is inserted into the vicinity of the filtering device, into the trap element whereby the trapping members are temporarily outwardly displaced enabling suction of the plaque debris. However, upon removal of the suction catheter, the trapping members return to their original position (owing their elasticity) in which they extend inwardly within the trap element.